The present invention relates generally to tracking items using radio frequency identification tags and, more particularly, to determination of distances between tags and signposts, and of the location of the signposts.
According to known techniques for tracking items, a device known as a radio frequency identification tag is mounted on each item, and radio frequency signals are used to communicate information between the tag and a receiver, which is referred to as a reader. Existing tags provide limited accuracy with respect to determining distances between tags and signposts, and in determining the specific location of the tag. For example, existing systems may determine the distance to between the tag and reader based on the magnitude of the signal emitted by the tag, as received at the reader. However, similar existing tags may transmit signals with slightly different magnitudes, and environmental factors may affect the magnitude of the signals transmitted by these tags. As a result, there is a large margin of error in the ability of the reader to accurately determine the distance to a tag based on the magnitude of the received signal.
Similarly, existing systems provide for crude measurements of distance based on the range of the signpost used in conjunction with the tag. However, these provide at best a rough estimate of the location of a tag to within the range of the signpost. Further, it may be even more difficult to determine the direction the tag is traveling using these known methods.